Lists a matrix of combinations of 1 to n variables in ascending order
combos(n)
an integer: the number of variables
a list containing
a matrix with zeroes in empty elements and 1 in column 1, 2 in column 2 ... n in column n for full elements
a matrix as for ragged, but with 1 in all full elements
Lists hierarchy of all possible combinations of n variables in ascending
order, starting with 1 variable, then all combinations of 2 variables,
and so on until the one combination with all n variables. This function
is used by all.regs
to structure the models required for
hierarchical partitioning.